Oscillator



1962 B. 1.. SNAVELY 3,049,678

OSCILLATOR Original Filed March 3, 1948 FIG.1.

INVENTOR. B. L. SNAVELY United States Patent 3,049,678 OSCILLATORBenjamin L. Snavely, Takoma Park, Md.

Original application Mar. 3, 1948, Ser. No. 12,843, new

Patent No. 3,028,757, dated Apr. 10, 1962. Divided and this applicationJune 24, 1957, Ser. No. 673,995

3 Claims. (Cl. 331-168) (Granted under Title 35, US. Code (1952), see.266) This invention may be manufactured and used by or for theGovernment of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

This is a divisional application of application for Electrical BridgeMeasuring Apparatus, Serial No. 12,843 filed March 3, 1948 by the sameinventor, and relates to an oscillator. More particularly the oscillatorof the present invention provides a source of very stable oscillationsfor applications where stability of the oscillation is of criticalimportance.

The oscillator of the present invention has a frequency control circuitconnected to a push-pull feedback circuit. The output of the push-pullcircuit is fed back to the control circuit by way of a voltage limitercircuit.

It is an object of this invention to provide an oscillator having a highdegree of stability.

Other objects and many of the attendant advantages of this inventionwill be appreciated readily as the same becomes understood by referenceto the following detailed description, when considered in connectionwith the accompanying drawings wherein:

FIG. 1 is a schematic drawing of the novel oscillator; and

FIG. 2 is a block diagram of said oscillator.

A stabilized oscillator comprising electron discharge tubes 70, 71, 46,47, and 76 and associated components is illustrated in FIG. 1. H

The frequency controlling L-C circuit of the aforementioned oscillatorincludes a center tapped inductor comprising inductances 64 and 65connected together in series, and having the junction therebetweengrounded at 10. Connected across the two inductors 64 and 65 is a tuningcapacitor 63, one terminal of capacitor 63 being connected by way ofresistor 61 to the control grid of oscillator tube 70,- which may be atriode of any con= venienttype. The other terminal of capacitor 63 iscon nected by way of resistor 62 to the control grid of tube 71, whichmay be a triode of a type similar to tube 70.

The cathode of tube 70 is connected through resistor 68 to ground,resistor 68 having a by-pass capacitor 66 connected in paralleltherewith, and the cathode of tube 71 is connected through resistor 69to ground, resistor 69 having a by-pass capacitor 67 connected inparallel therewith.

The anodes of tubes 70 and 71 are connected to load resistors 53 and 54'respectively, which have the other" ends thereof connected together andto the positive terminal of a battery 50, which has the negativeterminal thereof connected to ground;

The anode of tube '70 is connected byway of coupling capacitor 55 to thecontrol grid of electron discharge tube 46, which may be of anyconvenient type, in the embodiment shown and described herein, atetrode. Similarly, the anode of tube 71 is connected by couplingcapacitor ice Oil

56 to the control grid of tube 47, which is preferably of a type similarto tube 46. The control grids of tubes 46 and 47 are connected to groundthrough resistors 51 and 52 respectively, and the cathodes of tubes 46and 47 are connected to ground through resistors 48 and 49 respectively.The cathode of tube 46 is further connected through capacitor 57 inseries with resistor 59 to the grid of tube 70, and the cathode of tube47 is connected through capacitor 58 in series with resistor 60 to thecontrol grid of tube 71.

The control grid of tube 46 is connected by way of resistor 72 toinductor 65, while the control grid of tube 47 is connected by way ofresistor 73 to inductor 64.

The screen grids of tubes 46 and 47 are connected together and to thepositive terminal of battery 29 which has the negative terminal thereofgrounded at 10. The anode of tube 46 is connected to one end of primary13 while the other end of primary 13 is connected to the anode of tube47. The center tap of the primary 13 is connected to the aforementionedpositive terminal of battery 29. v

A regulator channel is provided, including tube 76, which may be atriode of any convenient type, having the control grid 78 thereofconnected by way of capac itor 80 to the cathode of tube 47, the controlgrid 78 also being connected by way of resistor 81 to ground 10.

The cathode 77 of tube 76 is connected by way of resistor to ground. Theanode 79 of tube 76 is connected by way of resistor 94 to the positiveterminal of battery 99 which has the negative terminal thereof connectedto ground. Anode 79 is further connected by way of capacitor 93,resistor 92, capacitor 82, and resistor 83,- connected in series in theorder named, to inductor 65. The junction between resistor 92 andcapacitor 82 is connected to a pair of rec'tifiers 90 and 91. The otherterminal of rectifier 91 is connected to ground 10, and the otherterminal of rectifier 90 is connected by way of capacitor 89 to ground10. I

The junction between capacitor 89 and rectifier 90 is connected to thecenter arm of a potentiometer 86 which has one terminal thereofconnected by way of resistor 87 to ground, and which has the otherterminal thereof connectcd to one end'of resistor 85, the other end ofresistor 85 being connected to one terminal of gaseous discharge tube88, the other terminal of the gaseous discharge tube 88 being connectedto ground. The junction between resistor 85 and tube 88 is connected byway of resistor 84 to the positive terminal of battery 100, the otherterminal of the battery being connected to ground at 10 The operation ofthe above traced oscillator circuit may best be understood by referenceto FIG. 2, in which is' shown a simplified diagram thereof, theamplifier stage 193 thereof comprising tubes 70 and 71 of l theamplifier stage 194 thereof comprising tubes 46 and 47 of FIG. 1, andthe amplifier stage 195 including tube 76 of FIG. 1.

The oscillator of 2' comprises a frequency selective network includinginductors 64 and 65 and capacitor 63,: which is connected totheamplifier 193 which is preferably dcsigned to be substantially linearin its amplifying characteristics. The output of amplifier 193 is fed totwo amplifiers the butler amplifier 194 which feeds theprimary 13 ofbridge transformer 12, and a feedback amplifier 195. Both amplifiers 193and 194' are stabi lized by inverse feedback, in a manner to besubsequently more fully described in connection with FIG. 1. The outputof amplifier 195 is connected by way of aforementioned capacitor 93,resistor 92, capacitor 82, and resistor 83, to the frequency controllingnetwork. Capacitors 82 and 93 are blocking capacitors which isolate theD.-C. potentials in the various parts of the circuit. Their capacitativereactances are preferably small compared to the impedances of thecircuits in which they operate.

The junction Q between resistor 92 and capacitor 82 is connected toground through rectifier 91 and also to ground through rectifier 90 andbattery 100, the impedance of which is preferably small. The rectifiers,which may be of the copper oxide or any other convenient type, conductcurrent unidirectionally, for example, in the direction indicated by thearrows of the rectifiers. Battery 100 is of a polarity to oppose theflow of current in this direction.

In the operation of the circuit of FIG. 2, if the potential of point Qrises above the potential of battery 100, current flows throughrectifier 90 and battery 100 to ground, while if the potential at pointQ falls below ground potential, current flows through rectifier 91. Theimpedances presented to point Q by resistor 92 in series with the outputimpedance of amplifier 195, and the impedance presented to point Q byresistor 83 in series with the tuned circuit 6365, are made high bychoice of component values, and as a result, the rectifiers 90 and 91effectively limit the extreme potentials at point Q. After the signal inthe feedback channel attains a predetermined level, a further increasein the signal supplied to amplifier 195 produces slight, if any,additional excitation of the tuned circuit. Accordingly, the tunedcircuit is excited at substantially a constant level. As the shape ofthe voltage variation at Q approaches a square wave, the excitation ofamplifier 193 becomes more nearly constant.

Referring again to FIG. 1, some additional refinements over the circuitarrangement of FIG. 2 are provided. The network of resistors 84, 85, 87,and potentiometer 86 permits adjustment of the operating voltage atpoint Q of the circuit, while the gaseous discharge tube 88 providesadditional voltage regulation for the point at which it is connected.Also, it is noted that cathode resistors 48 and 49 are unbypassed toprovide some degeneration and stabilization, and that inverse feedbackis provided by the aforementioned lead connection including capacitor 57and resistor 59 between the cathode of tube 46 and control grid of tube70, and the lead connection including capacitor 58 and resistor 60between the cathode of tube 47 and the control grid of tube 71. Cathoderesistor 49 alsoprovides coupling for securing a voltage for applicationto tribe 76, and the use of the unbypassed cathode resistors 48 and 49result in a high impedance presented to primary 13, with resultantincrease in the stability and sensitivity of operation of the bridge. Byproperly proportioning the resistors 72 and 73 with respect to resistors51 and 52 respectively, the output of the oscillator may be made nearlyindependent of the heater voltages applied to the tubes 70, 71,46, and47.

I Obviously many modifications and variations of the present inventionare possible .in the light of the above teachings. It is therefore to beunderstood that Within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

, What is claimed as new and desired to-be secured by Letters Patent ofthe United States is:

1. An oscillator comprising, in combination, a split inductance tunedcircuit having the center point of the inductance maintained at groundpotential, a first pair of electron discharge tubes each having ananode, control grid, and cathode, resistive electrical connectionsbetween the control grids and the ends of said inductance respectively,circuit means including a source of anode potential connected betweenboth said anodes and both said cathodes and having a point thereinmaintained at ground potential, a second pair of electron dischargetubes each having an anode, cathode, and control grid, a pair ofcoupling devices connected between the anodes of said first pair oftubes and the grids of said second pair of tubes respectively, biasingmeans for said second pair of tubes, a utilization circuit including asource of anode potential connected to the anodes of said second pair ofelectron discharge tubes, a pair of decoupling circuit devices connectedbetween the control grids of said first pair of tubes and the cathodesof said second pair of tubes respectively, resistive connections betweenthe control grids of said second pair of tubes and the respective endsof said inductance, and feedback means including a feedback amplifierintercoupling said second pair of electron discharge tubes and saidtuned circuit. a

2. An oscillator comprising a frequency determinative tuned network, afirst pair of electron tubes arranged in a push-pull amplifierconfiguration, a first pair of resistances, each of which interconnectsone end of said tuned network with the control grid of one of said firstpair of tubes, a second pair of electron tubes arranged in a pushpullamplifier configuration, a pair of R-C coupling networks, each of whichinterconnects the anode of one of said first pair of tubes and thecontrol grid of one of said second pair of tubes, a pair of R-C inversefeedback networks, each of which interconnects the control grid of saidone of the tubes of said first pair of tubes to the cathode of said oneof the tubes of said second pair of tubes, a second pair of resistances,each of which interconnects the control grid of one of said second pairof tubes and the end of said tuned network coupled to the control gridof the other one of said first pair of tubes, and a regenerativefeedback circuit coupled between the cathode of one of said second pairof tubes and one end of said tuned network, said feedback circuitincluding means for selectively adjusting the operating level of saidfeedback circuit, and means for regulating the magnitude of the feedbackenergy correlative to the operating level of said feedback circuit.

3. An oscillator comprising a frequency determinative network includinga parallel connected condenser and inductance, the center of saidinductance being maintained at ground potential, a first pair ofelectron tubes each having at least an anode, cathode, and control grid,a pair of parallel coupled resistance and capacitance networks, each ofwhich is disposed between the cathode of one of said first pair of tubesand ground potential, a pair of resistances each of which interconnectsone end of said frequency determinative network and the control grid ofone of said first pair of tubes, an output circuit coupled between theanodes of said first pair of tubes, said output circuit including a pairof serially connected resistors and a potential energy source, a secondpair of electron tubes each having at least an anode, cathode, andcontrol grid, a pair of serially coupled resistances interconnecting thecathodes of said second pair of tubes, the juncture of said last recitedpair of serially coupled resistances being maintained at groundpotential, a pair of R-C coupling networks, each of which interconnectsthe anode of one of said first pair of tubes and the control grid of oneof said second pair of tubes, an output circuit coupled between theanodes of said second pair of tubes, said last recited output circuitincluding a transformer winding and a potential energy source, a pair ofR-C inverse feedback networks each of which interconnects the cathode ofthe one of said second pair of'tubes and the control grid of the one ofsaid first pair of tubes interconnected by one of said R-C couplingnetworks, a pair of resistance paths each of which interconnects thecontrol grid of one of said second pair of tubes and the end of saidfrequency determinative network coupled to the control grid of the oneof said first pair of tubes connected to the other one of said secondpair of tubes by one of said R-C coupling networks, and feedback circuitmeans for effecting excitation of said frequency determinative network,said feedback circuit means including an amplifier stage having anelectron tube, means for coupling the control grid of said last recitedtube to the cathode of one of said second pair of tubes, means forcoupling the anode of said last recited tube to one end of saidfrequency determinative network, an amplitude limiting network coupledto said amplifier stage for regulating the level of the feedback energyto said frequency determinative network,

References Cited in the file of this patent UNITED STATES PATENTS DaileyMay 4, 1943 Detuno Oct. 12, 1948

